1. Field of the Invention
The present invention relates to a signal processor for encoding and decoding various kinds of data, particularly, image data.
2. Related Background Art
Various types of apparatuses have been developed to enable to transmit data at a relatively low transmission rate by encoding huge volumes of various data to decrease the volumes of data.
For example, for a digital VTR for recording image data in a recording medium such as a magnetic tape, there has been established a standard which specifies to compress input image data of approximately 124 MBps to approximately 25 MBps as large as ⅕ of the former volume.
In the digital VTR based on such standard as described above, the input data is quantized after DCT conversion and compressed by variable-length encoding the quantized data. In addition, the quantizing step for quantizing the data is varied in accordance with various parameters and the rate is controlled so that the volume of data which has been variable-length encoded is fixed.
The MPEG standard, which stipulates compression of input image data by using forecast encoding with interframe shift compensation and further compression of the image data by using DCT, quantizing and variable-length encoding as described above, is currently being established and various devices such as a CD-ROM and others which conform to this standard are developed.
An encoding/decoding device used in various apparatuses as described above uses a plurality of independent memories.
That is, for example, in a case of the digital VTR, a video memory for tentatively storing input image data and a track memory for storing coded data for which encoding has been completed before recording are required and, in the prior art, these memories have been independently provided.
An apparatus based on the MPEG standard is provided with a plurality of independent memories such as input buffer memories and reference buffer memories for compensating movement.
However, if a plurality of such memories are separately provided and independently controlled, such provision of the memories has been a cause of increased costs of the signal processor as a whole.